1. Field of the Invention
The present invention relates to a process for producing petrochemicals, using as a metallosilicate catalyst whose main cavity is defined by a ten-oxygen-membered ring.
2. Background Art
Since metallosilicatesxe2x80x94xe2x80x9cmetallosilicatesxe2x80x9d is herein a general term for aluminosilicates and their analogues in which aluminum atoms contained in the aluminosilicate framework are replaced with other metalsxe2x80x94have solid acidity. For that reason, they have conventionally been used as catalysts for hydrocarbon conversion reactions such as catalytic cracking, hydrocracking, disproportionation and isomerization, and various chemical reactions such as chemical synthesis reactions. A metallosilicate is present as a crystal having stereoregular structure in which oxygen atom is shared by a SiO4 tetrahedron and an MO4 (M is Al or any other metal atom) tetrahedron to form a three-dimensional network. In such a crystal, a ring composed of Si, O and M atoms, characteristic of the above linkage forms a cavity.
Metallosilicates show various solid acidities depending upon, for example, the type of metallosilicate and the coexisting cation, and have their own characteristic cavities. Moreover, the particle diameters of metallosilicates are controllable, and various modifications of metallosilicates are possible. Therefore, metallosilicates suitable as catalysts for specific chemical reactions have respectively been developed and used. For instance, among metallosilicates in which M is aluminum, that is, aluminosilicates, X- or Y-type aluminosilicate called faujasite is used, for example, as a catalyst for catalytic cracking or hydrocracking in petroleum refining; mordenite is used, for example, as a disproportionation or isomerization catalyst; and ZSM-5 is used as a catalyst for the synthesis of gasoline from methanol, or for various chemical synthesis reactions. Further, metallosilicates in which M is a metal atom other than aluminum are used as catalysts, for example, for the aromatization of light naphtha.
On the other hand, there is a demand for zeolite catalysts that show great specificity and high selectivity in specific chemical reactions. 2,6-Dimethylnaphthalene, for instance, can be produced by the isomerization reaction of a dimethylnaphthalene. It has been known that, although the isomerization of a dimethylnaphthalene, where methyl group is transferred from the xcex1-position to the adjacent xcex2-position and vice versa, can readily be attained, it is difficult to conduct isomerization of other types (Fries rule). It has therefore been difficult to isomerize a dimethylnaphthalene included in one of the following four groups of (1)-(4) to one included in any of the other groups:
(1) the group of 2,6-dimethylnaphthalene: 2,6-dimethylnaphthalene, 1,6-dimethylnaphthalene and 1,5-dimethylnaphthalene;
(2) the group of 2,7-dimethylnaphthalene: 2,7-dimethylnaphthalene, 1,7-dimethylnaphthalene and 1,8-dimethylnaphthalene;
(3) the group of 1,4-dimethylnaphthalene: 1,3-dimethylnaphthalene, 1,4-dimethylnaphthalene and 2,3-dimethylnaphthalene; and
(4) the group of 1,2-dimethylnaphthalene: 1,2-dimethylnaphthalene.
Various methods for isomerizing a dimethylnaphthalene have been proposed so far: for instance, a method in which a dimethylnaphthalene included in one of the above described four groups is isomerized to one included in the same group by using, as a catalyst, mordenite-type zeolite (e.g., Japanese Patent Laid-Open Publications No. 47020/1980 and No. 298675/1994); and a method in which a dimethylnaphthalene included in the group of 2,6-dimethylnaphthalene is isomerized to one included in this group by using, as a catalyst, faujasite-type zeolite represented by Y-type zeolite (e.g., Publication No. 500052/1991 of Japanese Translation of PCT Patent Application).
Further, a method using a pentasil-type crystalline aluminosilicate catalyst, the entrance of the main cavity of this aluminosilicate being defined by a ten-oxygen-membered ring, has been proposed as a method for isomerizing a dimethylnaphthalene included in the group of 2,7-dimethyl-naphthalene to one included in the group of 2,6-dimethylnaphthalene (e.g., Japanese Patent Laid-Open Publication No.88433/1984). There has also been proposed, as a method for isomerizing a dimethylnaphthalene included in the group of 2,3-dimethylnaphthalene to one included in the group of 2,7-dimethylnaphthalene or of 2,6-dimethylnaphthalene, a method in which a pentasil-type crystalline aluminosilicate composed of particles containing 50% by volume or more of such particles whose secondary particles have diameters smaller than 5 xcexcm is used as a catalyst in order to increase the efficiency of isomerization between two dimethylnaphthalenes included in different groups (e.g., Japanese Patent Laid-Open Publication No. 255139/1993).
Furthermore, there is a report on the studies in the relationship between the particle diameters of crystals and catalytic performance, in the correlation between the distribution of acid centers present on the internal or external surfaces of crystals and shape selectivity, and in the shape-selective isomerization of dimethylnaphthalenes (xe2x80x9cEffects of Particle Diameters of Crystals of H-ZSM-5 Catalyst on the Isomerization of Dimethylnaphthalenesxe2x80x9d, 78th CATSJ Meeting Abstracts: Vol. 38, No. 6, 1966, No. 4, B05, 474-477 (1996)). In addition, a process for rapidly producing a zeolite catalyst has been reported (T, Inui, xe2x80x9cMechanism of Rapid Zeolite Crystallization and Its Applications to Catalyst Synthesisxe2x80x9d, Zeolite Synthesis, ACS Symp. Series, 398, Chapter 33, 1989, American Chemical Society).
With respect to poisoning of zeolite catalysts on the external surfaces of their crystals and in their internal cavities, there is a report on poisoning of HZSM-5 by quinolines on its external surface (S. Namba, et al., Journal of Catalysis, 88, 505-508(1984)).
We found the following: a metallosilicate catalyst that comprises a metallosilicate having a main cavity defined by a ten-oxygen-membered ring, that is in the form of aggregates of fine crystals of the metallosilicate, the external surface area of the aggregate being in a specific range, and that has been treated to inactivate acid centers present on the external surfaces of the fine crystals until the rate constant basic value becomes a predetermined value shows great reaction specificity and high shape selectivity in various chemical reactions, and achieves high reaction efficiency and high degrees of conversion to remarkably increase the yields of desired products. The present invention.,is based on this finding.
An object of the present invention is therefore to provide a process for producing petrochemicals, using a metallosilicate catalyst that comprises a metallosilicate having a main cavity defined by a ten-oxygen-membered ring and that can increase the activity of various chemical reactions.
One aspect of the present invention is a process for producing 2,6-dimethylnaphthalene by subjecting 2,7-dimethylnaphthalene to an isomerization reaction, wherein the isomerization reaction is carried out by the use of a metallosilicate catalyst that comprises a metallosilicate having a main cavity defined by a ten-oxygen-membered ring, that is in the form of aggregates of fine crystals of the metallosilicate, the external surface area of the aggregate as calculated from t-plot analysis made in the nitrogen adsorption method being 25 m2/g or more, and that has been treated to inactivate acid centers present on the external surfaces of the fine crystals until the rate constant basic value N becomes 0.5 or less.
Metallosilicate Catalyst
The metallosilicate catalyst for use in the present invention is a metallosilicate catalyst that comprises a metallosilicate having a main cavity defined by a ten-oxygen-membered ring, that is in the form of aggregates of fine crystals of the metallosilicate, the external surface area of the aggregate as calculated from t-plot analysis made in the nitrogen adsorption method being25 m2/g or more, and that has been treated to inactivate acid centers present on the external surfaces of the fine crystals until the rate constant basic value N becomes 0.5 or less.
The metallosilicate catalyst for use in the present invention shows great reaction specificity and high shape selectivity in various chemical reactions, and can improve reaction activity and production efficiency to increase the yields of desired products. The reason why the metallosilicate catalyst has such advantageous properties has not yet been clarified. However, it is firstly assumed as follows: since aggregates of fine crystals of a metallosilicate, the external surface area of the aggregate as calculated from t-plot analysis made in the nitrogen adsorption method being 25 m2/g or more are used as the catalyst, the effective surface area of the catalyst that is the entrances of the cavities in the fine crystals, each defined by a ten-oxygen-membered ring is increased; as a result, the cavities in the crystals can effectively be utilized, and the reaction efficiency inside the cavities is thus increased. Further, it is also assumed that, since acid centers present on the external surfaces of the fine crystals are inactivated until the rate constant basic value N becomes 0.5 or less, side reactions do not occur at these acid centers. Therefore, it seems that both the shape selectivity and the reaction efficiency inside the cavities in the crystals are improved because the above two factors are well balanced.
An aluminosilicate or a metallosilicate containing a metal other than aluminum, having a main cavity defined by a ten-oxygen-membered ring can be used as the metallosilicate in the metallosilicate catalyst for use in the present invention. Typical examples of such metallosilicates include aluminosilicates having main cavities defined by ten-oxygen-membered rings, such as ZSM-5 and ZSM-11, and metallosilicates having main cavities defined by ten-oxygen-membered rings, such as ferri(Fe)silicate, gallo(Ga)silicate and boro(B)silicate. These metallosilicates may form a crystal either singly or in combination of two or more members.
The metallosilicate catalyst for use in the present invention is in the form of aggregates of fine crystals of a metallosilicate, the aggregate being composed of fine metallosilicate crystals and moderate voids formed between these fine crystals. The fine crystal of a metallosilicate may be in any shape, for example, in the shape of a fine pillar, a thin layer, a pillar, a layer, a cube or a rectangular parallelpiped. It is preferable that the fine crystal be in the shape of a fine pillar or a thin layer. In the present invention, a fine crystal in any shape can be used, but the length of its short side or its thickness is required to be approximately 0.5 xcexcm or less, preferably about 0.2 xcexcm or less, more preferably about 0.1 xcexcm or less.
These fine crystals aggregate to be an aggregate of secondary, tertiary, or higher-order structure. There is no particular limitation on the size of this aggregate. In general, however, this size is in the range of about 1 to 8 xcexcm. It is preferable that voids (about 10 nm to about 100 nm) be present between the crystals in the aggregate. However, not all of the fine crystals in the aggregate are separated from one another, and the aggregate as a whole has strength that is generally required for a solid catalyst. For instance, in the case of an aggregate of plate-like crystals, the aggregate is in such a state that a large number of plate-like crystals in different sizes are laminated.
For this reason, in the metallosilicate catalyst for use in the present invention, the external surface area of the aggregate of fine crystals is defined not as the sum total of the external surface areas of the individual fine crystals obtainable by calculation, but as the effective surface area of the aggregate that varies depending upon the state of aggregation of the fine crystals. Specifically, the external surface area of the aggregate of fine crystals is determined by t-plot analysis made in the nitrogen adsorption method. We found that the catalytic activity of the metallosilicate catalyst can be evaluated by the external surface area of the aggregate of fine crystals determined by the nitrogen adsorption method more linearly than by the size of the aggregate or of the fine crystals obtained by calculation from X-ray diffraction analysis, which is used ordinarily.
According to a preferred embodiment of the present invention, it is preferable to use, as the metallosilicate catalyst, aggregates of fine crystals of a metallosilicate, the external surface area of the aggregate as calculated from t-plot analysis made in the nitrogen adsorption method being 25 m2/g or more, preferably 30 m2/g or more, more preferably 35 m2/g or more.
In this specification, the xe2x80x9cnitrogen adsorption methodxe2x80x9d is the conventional nitrogen adsorption method usually used for measuring the specific surface area of a porous material. This method of measurement is a conventional method for measuring a BET surface area, and can be effected in the following manner: a sample that has been dried is placed in a glass-made cell, and deaerated under vacuum; nitrogen gas is introduced into this cell little by little at a temperature of 77xc2x0 K; and the equilibrium pressure and the amount of nitrogen adsorbed are measured. t-Plot analysis is performed for this porous sample by the use of the adsorption isotherm obtained from the above-described method of measurement.
The xe2x80x9ct-plot analysisxe2x80x9d is performed to analyze the data obtained from the above-described nitrogen adsorption method. This analysis uses a t-curve that is a standard isotherm obtainable by plotting the thickness t of an adsorption film against relative pressure p/p0(the t-plot method by Lippens de Boer). Specifically, a t-curve is represented by the following equation (I):
t=(V/Vm)"sgr"xe2x80x83xe2x80x83(I)
wherein t represents the thickness of an adsorption film, V/Vmrepresents the average number of adsorption layers contained in the adsorption film, and a represents the thickness of a monomolecular layer.
A t-plot is a plot of the amount v of nitrogen adsorbed versus the thickness t of an adsorption film, and obtainable herein as the t-plot is a straight line bending at the t value that corresponds to the diameter of a pore. From the gradient of this straight line on the higher-pressure side, that is, on the greater-t-value side, the external surface area of the porous sample can be determined. The measurement in accordance with the nitrogen adsorption method, and the analyses of the BET specific surface area and of the external surface area obtained from the t-plot can be made by a commercially available nitrogen adsorption analyzer (e.g., xe2x80x9cBellsorp 28xe2x80x9d manufactured by Nippon Bell Kabushiki Kaisha, Japan).
The metallosilicate catalyst for use in the present invention comprises a metallosilicate whose main cavity is defined by a ten-oxygen-membered ring. The xe2x80x9cmain cavity defined by a ten-oxygen-membered ringxe2x80x9d herein means a major cavity among those cavities present in the metallosilicate, having an entrance formed by a ten-oxygen-membered ring. By the xe2x80x9cten-oxygen-membered ringxe2x80x9d is herein meant a ring composed of silicon or metallic atoms and oxygen atoms, the number of oxygen atoms constituting the ring being 10. The diameter of the main cavity defined by a ten-oxygen-membered ring is said to be approximately 0.6 nm.
In the present invention, the metallosilicate catalyst that comprises a metallosilicate having a main cavity defined by a ten-oxygen-membered ring and that is in the form of aggregates of fine crystals of the metallosilicate is used after being subjected to such treatment that acid centers present on the external surfaces of the fine crystals are inactivated until the rate constant basic value N becomes 0.5 or less, preferably 0.3 or less, more preferably 0.2 or less.
Typical methods for inactivating acid centers present on the external surfaces of fine crystals, useful in the present invention include the following: a method in which an organic base whose molecular size is larger than the diameter of the main cavity defined by a ten-oxygen-membered ring, for instance,sa quinoline such as dimethylquinoline (e.g., 2,4-dimethylquinoline), trimethylquinoline or xcex2-naphthoquinoline is added, a silica-coating method, for example, a method in which!tetraethyl or tetramethyl silicate is deposited on the metallosilicate catalyst) and the resultant is then subjected to thermal decomposition; a method in which an inorganic base compound (e.g., a compound of Ba, Mg, or the like) is added; a method in which aluminum-removing treatment is conducted by the use of silicon tetrachloride; and any combination of these methods. In a preferred embodiment of the present invention, a method in which a quinoline, especially 2,4-dimethylquinoline, is added, and a silica-coating method are preferred.
An index for inactivation is obtained in the following manner: the reaction of triisopropylbenzene (incapable of entering into the main cavity in the fine crystal, defined by a ten-oxygen-membered ring) or ethylbenzene (capable of entering into the main cavity in the fine crystal, defined by a ten-oxygen-membered ring) is carried out over the metallosilicate catalyst before or after being subjected to the inactivation treatment and in a fixed-bed reactor; and the degree of conversion of the triisopropylbenzene and that of the ethylbenzene are introduced to the following equation (II) to calculate the rate-constant basic value N:                     N        =                                            [                                                {                                      -                                          ln                      ⁡                                              (                                                  1                          -                          X                                                )                                                                              }                                /                                  {                                      -                                          ln                      ⁡                                              (                                                  1                          -                                                      X                            0                                                                          )                                                                              }                                            ]                        ⁢            TIPB                                              [                                                {                                      -                                          ln                      ⁡                                              (                                                  1                          -                          X                                                )                                                                              }                                /                                  {                                      -                                          ln                      ⁡                                              (                                                  1                          -                                                      X                            0                                                                          )                                                                              }                                            ]                        ⁢            EB                                              (        II        )            
wherein X represents the degree of conversion in the case where the catalyst after being subjected to the inactivation treatment was used, X0 represents the degree of conversion in the case where the catalyst before being subjected to the inactivation treatment was used, TIPB means triisopropylbenzene, and EB means ethylbenzene.
When this rate constant basic value N is used, the influences of differences in temperature and contact time are eliminated. The degree of inactivation of the catalyst can thus be evaluated objectively as reaction rate ratio.
A preferred method of measurement useful for obtaining the rate constant basic value N by calculation is a method using a fixed-bed reactor which is controlled so that a constant reaction temperature through the bed is realized. For instance, in the case where a fixed-bed reactor having an inner diameter of 0.8 cm is used, the following method of measurement can be employed: 1 g of a metallosilicate catalyst is charged to the isothermal fixed-bed reactor, and triisopropylbenzene or ethylbenzene is fed, at 400xc2x0 C. under normal pressures, to the fixed-bed reactor at a feed rate of 2.5 g/h while feeding nitrogen as a carrier gas at a feed rate of 1.79 NL/h; after 30 minutes, the oil produced is fully recovered over 15 minutes, and the degree of conversion of the feedstock is obtained with a gas chromatograph.
Process for Producing Metallosilicate
A metallosilicate having a main cavity defined by a ten-oxygen-membered ring, which is an essential component of the metallosilicate catalyst for use in the present invention, can be produced in accordance with the process described below in detail.
In one embodiment of the present invention, ZSM- 5, one aluminosilicate having a main cavity defined by a ten-oxygen-membered ring, can be produced by heating, to 100-175xc2x0 C. in an autoclave, a gelled mixture of starting compounds whose compositions are in the ranges shown in Table 1 (see xe2x80x9cZeoraito no Kagaku to Oyo (Science and Applications of Zeolite)xe2x80x9d, edited by Hiroo Tominaga, page 87, Kodansha Scientific, Japan (1987)).
According to a preferred embodiment of the present invention, the metallosilicate catalyst for use in the present invention can be synthesized in accordance with the xe2x80x9crapid crystallization methodxe2x80x9d described in the literature by T, Inui (xe2x80x9cMechanism of Rapid Zeolite Crystallization and Its Applications to Catalyst Synthesisxe2x80x9d, chapter 33, 1989, American Chemical Society). By this rapid crystallization method, aggregates of fine crystals of a metallosilicate having a main cavity defined by a ten-oxygen-membered ring, the external surface area of the aggregate being large can be produced in a shorter time than by other production methods. Further, as compared with metallosilicates produced by other methods, a metallosilicate produced by this method has a small number of acid centers on the external surface of its crystal, and the activity of this external surface is also low. The outline of the xe2x80x9crapid crystallization methodxe2x80x9d is as follows.
Liquids A and B having the compositions shown in Table 2 are added to liquid C to form a gel while maintaining the pH of the mixture at 9-11, and this gel is subjected to centrifugal separation. The precipitate is taken out, ground in a mortar, and subjected again to centrifugal separation. This operation is repeated two or three times, and the precipitate (D) is recovered. Separately, liquids Axe2x80x2 and Bxe2x80x2 having the compositions shown in Table 3 are added to liquid Cxe2x80x2 to form a gel. This gel is centrifuged, and the supernatant liquid (E) is recovered. The precipitate D is added to this supernatant liquid E, and the mixture is placed in an autoclave. The temperature of the mixture is raised from normal temperatures to 1600xc2x0 C. at an average heat-up rate of 1xc2x0 C./min, and from 160 to 210xc2x0 C. at a heat-up rate of approximately 0.2xc2x0 C./min. After maintaining at 210xc2x0 C. for 25 minutes, the mixture is cooled, and filtered. The crystals collected are washed with water, dried, and then calcined to yield ZSM-5, a metallosilicate according to the present invention, having a main cavity defined by a ten-oxygen-membered ring; this is in the form of aggregates of the crystals of the metallosilicate, the external surface area of the aggregate being in a specific range. In this method, aluminum nitrate can be used instead of aluminum sulfate as a source of aluminum. The source of aluminum is used in an amount calculated from the Si/Al ratio in ZSM-5 to be produced. It is also possible to produce ferrisilicate by using, in this xe2x80x9crapid crystallization methodxe2x80x9d, a source of iron (e.g., iron nitrate) instead of the source of aluminum.
By inactivating acid centers present on the external surfaces of the above-obtained fine crystals of the metallosilicate until the rate constant basic value falls in a specific range, it is possible to make the metallosilicate into a metallosilicate catalyst according to the present invention. The metallosilicate catalyst according to the present invention, comprising the metallosilicate having a main cavity defined by a ten-oxygen-membered ring may be subjected to proper treatment before it is used for various chemical reactions. In a preferred embodiment of the present invention, the metallosilicate catalyst according to the present invention may be used after it is ion-exchanged to proton type. The ion exchange of the catalyst to proton type can be effected by the use of, for instance, an aqueous solution of ammonium chloride.
Process for Producing 2.6-Dimethylnaphthalene (Isomerization Reaction)
In this production process of the present invention, not only 2,7-dimethylnaphthalene itself but also stock oil containing 2,7-dimethyl-naphthalene in a significant amount can be used as feedstock. It is also possible to use 2,7-dimethylnaphthalene produced by the process for producing a dialkylnaphthalene according to the present invention, which will be described later in detail.
In this production process of the invention, an isomerization reaction is carried out. This reaction is characterized by using, as a catalyst, a metallosilicate catalyst according to the present invention, comprising a metallosilicate having a main cavity defined by a ten-oxygen-membered ring.
The reaction temperature in this production process is preferably between 200xc2x0 C. and 500xc2x0 C., more preferably between 250xc2x0 C. and 450xc2x0 C. When the isomerization reaction is carried out at a temperature of 200xc2x0 C. or higher, the reaction proceeds thoroughly, and 2,6-dimethylnaphthalene is produced in an increased yield. When the reaction is carried out at a temperature of 500xc2x0 C. or lower, undesirable side reactions do not occur. Moreover, it is not necessary to install heat-resistant equipment suitable for high-temperature reactions, so that such a reaction temperature is favorable also from an economical point of view.
In this production process, the reaction is carried out at a pressure preferably between normal pressures and 50 kg/cm2, more preferably between normal pressures and 30 kg/cm2. By carrying out the reaction at a pressure of 50 kg/cm2 or lower, it is possible to decrease the power required for compression systems. Moreover, it is unnecessary to install high-pressure equipment. Such a pressure is thus favorable also from an economical point of view.
Any reactor of fixed, moving or fluidized bed type can be used in this production process of the invention.
From the product produced by this production process, 2,6-dimethylnaphthalene is isolated and recovered. The isolation/recovery step can be conducted, for example, through a conventional distillation, adsorption or crystallization operation, or a combination thereof.
Process for Producing Dialkylnaphthalene
In this production process of the invention, it is possible to use, as feedstock, not only methylnaphthalene, naphthalene or a mixture of these compounds, but also stock oil containing methylnaphthalene and/or naphthalene in a significant amount. For example, there may be used methylnaphthalene (preferably xcex2-methylnaphthalene) or naphthalene produced by the process for producing methylnaphthalene or naphthalene according to the present invention, which will be described later in detail.
In this production process of the invention, an alkylation or transalkylation reaction is carried out. These reactions are characterized by using, as a catalyst, a metallosilicate catalyst of the present invention, comprising a metallosilicate having a main cavity defined by a ten-oxygen-membered ring.
In this production process, an alkylation or transalkylation agent is used. Typical examples of alkylation or transalkylation agents include arenes, alkenes, alcohols, esters, ethers and alkyl halides. Preferable alkylation or transalkylation agents are as follows.
Typical examples of arenes include arenes containing at least one alkyl group having not more than 5 carbon atoms. Preferable arenes are alkylbenzenes and/or alkylnaphthalenes containing at least one alkyl group having not more than 2 carbon atoms.
Preferable examples of alkenes are alkenes having not more than 5 carbon atoms; and ethylene is more preferred.
Typical examples of alcohols include alcohols containing at least one alkyl group having not more than 5 carbon atoms. Primary alcohols having at least either methyl or ethyl group are preferred, and methyl or ethyl alcohol is more preferred.
Typical examples of esters or ethers include those ones containing at least one alkyl group having not more than 5 carbon atoms. Esters or ethers having at least either methyl or ethyl group are preferred, and dimethyl carbonate is more preferred.
The reaction temperature in this production process is preferably from 200 to 550xc2x0 C., more preferably from 250 to 490xc2x0 C. When the alkylation or transalkylation reaction is carried out at a temperature of 200xc2x0 C. or higher, the reaction proceeds thoroughly, and a dialkylnaphthalene is produced in an increased yield. When the reaction is carried out at a temperature of 550xc2x0 C. or lower, the reaction never proceeds excessively, so that unfavorable side reactions do not occur. Moreover, it is not necessary to install heat-resistant equipment suitable for high-temperature reactions. Therefore, such a reaction temperature is favorable also from an economical point of view.
To particularly increase the yields of 2,6-dialkylnaphthalenes, it is necessary to properly establish temperature conditions. By making the temperature conditions proper, it is possible to carry out the alkylation or transalkylation reaction without causing side reactions.
In this production process, the reaction is carried out at a pressure preferably between normal pressures and 50 kg/cm2, more preferably between normal pressures and 30 kg/cm2. By carrying out the reaction at a pressure of 50 kg/cm2 or lower, it is possible to decrease the power required for compression systems. Moreover, it is not necessary to install high-pressure equipment. Such a reaction pressure is thus favorable also from an economical point of view.
Any reactor that can be used in the aforementioned process for producing 2,6-dimethylnaphthalene can be used in this production process of the invention.
From the product produced by this production process, a dialkylnaphthalene (preferably dimethylnaphthalene) is isolated and recovered. The isolation/recovery step can be conducted through a conventional distillation operation or the like.
Process for Producing 2,6-Dimethylnaphthalene
According to one embodiment of the present invention, 2,6-dimethylnaphthalene can be produced, starting from methylnaphthalene or naphthalene, by using the aforementioned process for producing a dialkylnaphthalene and the previously described process for producing 2,6-dimethylnaphthalene (isomerization reaction) in combination. Those catalysts, reaction conditions and reactors that are suitable for these two production processes can be used in this production process.
According to a preferred embodiment of the present invention, 2,6-dimethylnaphthalene can be produced by the combination use of the process for producing methylnaphthalene or naphthalene by subjecting an alkylnaphthalene to a hydrodealkylation reaction, which will be described later in detail, the above-described process for producing a dialkylnaphthalene, and the previously described process for producing 2,6-dimethylnaphthalene (isomerization reaction). Those catalysts, reaction conditions and reactors that are suitable for these three production processes can be used in this production process.
Process for Producing Methylnaphthalene or Naphthalene
Not only an alkylnaphthalene itself but also stock oil containing an alkylnaphthalene in a significant amount can be used as feedstock in this process. Typical examples of useful feedstock include a fraction of cracked or reformed oil of petroleum refining and/or petroleum refining products, for example, cracked or reformed distillates obtained from the catalytic cracking, thermal cracking or catalytic reforming of petroleum, or from a process for producing ethylene from petroleum; coal tar distillate; liquefied coal oil; and mixtures thereof. of the above-described cracked or reformed oil fractions of petroleum and/or refined petroleum products, those fractions having boiling points of 170 to 300xc2x0 C., more preferably 210 to 280xc2x0 C. are preferred as the stock oil for use in this production process of the present invention. More preferable stock oil is a cracked gas oil fraction having boiling points of 210 to 280xc2x0 C. obtained from the catalytic cracking of petroleum.
The stock oil can contain such impurities as sulfur-containing compounds, for example, benzothiophenes, nitrogen-containing compounds for example, quinolines and indoles, and oxygen-containing compounds, for example, phenols, benzofuran and dibenzofuran.
In this production process of the invention, a hydrodealkylation reaction is carried out. For this reaction, zeolite or a zeolite composition, for example, a catalyst for the fluid catalytic cracking (FCC) of petroleum, can be used as a catalyst. It is also possible to use such a catalyst that an active metallic component, and, if necessary, optional components are supported on a porous body having porous structure.
Any of metals such as vanadium (V), molybdenum (Mo), chromium (Cr), cobalt (Co), nickel (Ni), platinum (Pt), rhodium (Rh) and iridium (Ir), oxides or sulfides of these metals, and mixtures thereof can be used as the active metallic component.
The concentration of the active metallic component, calculated in terms of metal is preferably from 0.1 to 30% by weight, more preferably from 0.2 to 15% by weight.
Alumina, silica, silica alumina, kaolin, or a combination thereof is used as the porous body having porous structure. Particularly preferred are kaolin and alumina. Zeolite can be incorporated into this carrier to further increase the dealkylation activity.
The mean diameter of pores in the porous body having porous structure is preferably from 70 to 800 angstroms, more preferably from 80 to 700 angstroms.
Alkali metals, alkali earth metals, rare earth elements or the like may be used as the optional components in order to increase the heat resistance and selectivity of the catalyst.
A preferable catalyst for the hydrodealkylation reaction in the present invention is one whose active metallic component is vanadium (V) oxide or sulfide and whose carrier that supports the active metallic component is a porous body having porous structure, capable of fulfilling the above described requirements. Such a catalyst shows excellent desulfurizing activity even when coke is deposited on the catalyst.
The reaction temperature in this production process of the invention is preferably from 450 to 700xc2x0 C., more preferably from 500 to 670xc2x0 C. By carrying out the reaction at a temperature of 450xc2x0 C. or higher, it is possible to make the degrees of dealkylation and desulfurization higher, so that methylnaphthalene having improved quality can be obtained in an increased yield. When the hydrodealkylation reaction is carried out at a temperature of 700xc2x0 C. or lower, the reaction never proceeds excessively, and unfavorable side reactions do not take place. Moreover, investment in plant and equipment such as heat-resistant equipment suitable for high-temperature reactions is not required as long as the reaction is carried out at such a temperature.
When the hydrodealkylation reaction is carried out in this production process of the invention, the partial pressure of hydrogen is controlled to preferably 1xe2x89xa750 kg/cm2, more preferably 3-30 kg/cm2. By controlling the partial pressure of hydrogen to 1 kg/cm2 or higher, it is possible to make the degrees of hydrodealkylation and desulfurization higher, and to prevent the deposition of coke on the surface of the catalyst. By controlling the partial pressure of hydrogen to 50 kg/cm2 or lower, it is possible to prevent hydrocracking reaction that is induced by the hydrogenation of naphthalene ring. As a result, the reaction selectivity is increased, and the consumption of hydrogen is thus reduced.
In this production process of the invention, the contact time is preferably from 1 to 35 seconds, more preferably from 2 to 30 seconds. By making the contact time 1 second or longer, it is possible to attain higher degrees of dealkylation and desulfurization. By making the contact time 35 seconds or shorter, it is possible to prevent excessive progress of the dealkylation reaction. Moreover, it is not necessary to make the reactor larger, so that such a contact time requires less economical burden.
From the product produced by this production process of the invention, naphthalene, methylnaphthalene (preferably xcex2-methylnaphthalene), or a mixture thereof is isolated and recovered. The isolation/recovery step can be conducted through a conventional distillation operation or the like.
Any reactor of fixed, moving or fluidized bed type can be used for this production process of the invention. A reactor of fluidized bed type is particularly preferred. The reason for this is as follows: the thermal conductivity of such a reactor is high, and the temperature of the reaction system is thus maintained constant, so that even a reaction accompanying large heat of reaction, such as a hydrodealkylation reaction, proceeds smoothly; in addition, it is possible to continuously conduct both the removal of a degraded catalyst and the feeding of a regenerated or fresh catalyst.
A desirable fluidized-bed reactor is one having a plurality of fluidized beds composed of a reactor and a regenerator, a catalyst being circulated between these fluidized beds. A fluidized-bed reactor may be of any type such as dense phase type or riser type.